Human View

Summary

Fixes #11671 (5+ years old, 82 reactions).

When CSS files are used as webpack entry points, an unnecessary empty .js file is generated in the output alongside the CSS. This forces users to rely on third-party plugins like webpack-remove-empty-scripts.

Before

// webpack.config.js
entry: { styles: './src/styles.css' }
// Output: dist/styles.js (EMPTY) + dist/styles.css

After

// Output: dist/styles.css (only)

Root Cause

Two functions in JavascriptModulesPlugin.js cause this:

1. chunkHasJs() (line 83) returns true for any chunk with entry modules, without checking their source types. CSS-only entry modules have source type "css", not "javascript".

2. chunkHasRuntimeOrJs() (line 96) returns true when runtime modules exist. But runtime modules are always added to entry chunks — for CSS-only entries, the runtime has nothing to bootstrap.

Fix

• chunkHasJs(): Iterate entry modules and check their source types. Only return true when at least one entry module has JAVASCRIPT_TYPE.

• chunkHasRuntimeOrJs(): When runtime modules exist, check for JS non-entry modules first. If only runtime + entry modules, verify entry modules have JS source type. For standalone runtime chunks (optimization.runtimeChunk: true), keep JS emission since the bootstrap code is needed.

Changes

Edge Cases Verified

• CSS-only entry (web target): No JS file emitted
• CSS-only entry (node target): JS file still emitted (CSS modules export class names as JS on node)
• JS entry: Still emits JS normally
• Mixed JS+CSS entries: JS entry keeps .js, CSS entry drops empty .js
• optimization.runtimeChunk: true: Standalone runtime chunk keeps JS for bootstrap
• chunkHasJs as public API: Used by 5+ chunk loading modules — the change makes it more correct (CSS chunks truly don't have JS)
• All existing split-chunks, runtime, and CSS tests pass

Testing

• All only-entry test cases pass (7 configs)
• vendor-only-entrypoint (runtimeChunk: true) passes
• pure-css passes
• no-extra-runtime-with-asset-modules passes
• 0 new regressions (pre-existing failures are ESM infrastructure issues on main)

AI View (DCCE Protocol v1.0)

Metadata

• Generator: Claude (Anthropic) via Cursor IDE
• Methodology: AI-assisted development with human oversight and review

AI Contribution Summary

• Root cause analysis through code tracing
• Solution design and implementation
• Edge case analysis and verification

Verification Steps Performed

1. Reproduced the reported issue
2. Analyzed source code to identify root cause
3. Implemented and tested the fix

Human Review Guidance

• Verify the root cause analysis matches your understanding of the codebase
• Core changes are in: JavascriptModulesPlugin.js, lib/javascript/JavascriptModulesPlugin.js, test/configCases/asset-modules/only-entry/test.js
• Verify edge case coverage is complete

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